What practical functions did Sina and Compass have in ancient China?

In fact, these two things are similar. During the Warring States period, jade pickers often needed to take "Sina" with them for help and guidance. As for the exact shape and usage of Sina, according to Wang Chong's record in Lun Heng in the Eastern Han Dynasty, it should be carefully carved into the shape of a spoon with a natural magnet, and the south pole is located on the long handle of the spoon. In the process of carving, the center of gravity of the spoon needs to be located in the center of the bottom, plus four dimensions (namely, dry, Kun, Xun and Gen) and "eight"

The invention of compass has no exact time and inventor. Ceng Gongliang's General Theory of Martial Arts in the Northern Song Dynasty mentioned that "compass fish" was used to help identify the direction when marching. As for the "compass fish", it is a fish-like steel plate, five minutes wide and two inches long, with a sunken abdomen and a shape like a boat. After magnetization, it can float on the water to distinguish the north from the south.

According to historical records, the compass was first made by Sina in the Spring and Autumn Period.

The compass laid the foundation for human beings to identify the direction. It initiated human understanding of the geomagnetic field. Compasses are widely used in military operations, navigation, aviation, tourism and other fields.